Electric pointer clamp for indicating instruments



Dec. 15, 1953 A. G. OBERMAIER ELECTRIC'POINTER CLAMP FOR INDICATING INSTRUMENTS Filed May 19, 1951 2 Sheets-Sheet l a Q 2% w E W MN i u .bN m S H M ll w i c T m %N N y lm N l N o o INVENTOR.

Dec. 15, 1953 A. G. OBERMAIER ELECTRIC POINTER CLAMP FOR INDICATING INSTRUMENTS Filed May 19, 1951 2 Sheets-Sheet 2 Patented Dec. 15, 1953 it "STATES PATENT OFFICE ELECTRIC POINTER CLAMP oa INDICATING INSTRUMENTS 7 Alfred A, Obermaier, Park Ridge, 111., assignor to Illinois Testing Laboratories I na, Chicago, 111.; a corporation'of Illinois 8 C a ms- 1. The present invention relates t le tric wint r clam s for n icatin nst uments and is a ticularly sshcerhed th h p svi i n s animprovsd means. for holdi t s nt r Q h" i i ati nstrum n at an d s red in ci li s positi n s tha ts ihdisat oh W111 rsiheih constant, and can h read at a y i hs de irsi by the user, instead of requ n the ussr to b nresehtat the time the iIldiChiQI is ad i Qne. of the obj cts wi h inven on is e p vision at an .imnrovs ielsci p n r clamp o use hatin ihs rhm ht by m ans 9f whish the .lativsly li h poin r ca he h l in ny hd eatihs ms iqh wi hQht ama n iths pa nt r and ithhh s wa detracti from the accuracy of the instrument Another obj ct of the invention i t e pr v sion. at an imnroysd nq ht r lam n d ice which is adapted to 12 astua sd l tr c l and hich mam. .thersiqre, he ontro led by suita l isstr h sirs its and e ays withsut nece i y o sri mih .ahy .mahiia ohsraii hs h he intrihmshti another abject of the invention s t Dl'Q si hof an elect ic point r .h aihp hr i dicat n hst umshts whi h simp e in shhs uci sh durable, sans-bi of s ohomi al manhia thr and adapt d to hi hs iior a lo per d o im withou sheetin sub taht aily the ccura y or SeiiSitivityQf the instr men .Qther objects and aiivahtasss 9f the i nti n will he ap a ent i qih he fol owin des rihtish and the assohipanvi d awi gs n which s har characters oi re srehse ihd sat similar pa ts throughout the several views.

heierrihs t0 the tws shssts of drawi s asc ihpan ih h s sp ciii a ioh V Fig. 1 is a; view .psrsp ct ve of an elect ca ins rument smbodyin the ihventiQn, ShOW i i ohhesti h with a re a c uit for hhtr llih dampin a tion;

Fi 2 is a side e erat ohal i w of the devic i Fi 11;

Fig, 3 is adia rammatic illustration of the in-. rumshtahd i s Wirf g diagram, shown in c hneht oh with the terminal osts with which the ins rumen is (prefera ly provide Bsisr heto Fi l, l0 indicates in its entir ty an electrical vh sash ihs hstrum.ent(of the movih's 91. type w i h is provided with a vane s nin ement embodyin the inveni I hmeht movement ousin H is v, w i thsusual type f movin coil elehaht hhtsd hnoh jewel hearings, one of which is'carried by bridge I3,

Application May 19, 1951, Serial No. 227,195

In addition to the usual hair springs for ui ing the pointer M to zero position and for carrying current to the. moving coil, the instrument is provided with a, third spring [5 suitably insulated from the moving coil of the instrument, but. at the same potential with respect to the aluminum pointer tubing. A fine copper wire may be wou d about t po nt r sxt hdihs from this third. spring to the Va s o ai creasin h co d cti ty f the po ts M- he insulated wire IT ma h woun ut the poi tsniwhic s the usua csuhtsr aians hs s hbs s s at s nph ndhe fih insu atin w re I lead t a a e, 19 whi h is hhisrsd to the po nte oh its lqwsr ida ahd hich is qu te ccu a el s ace i s a se o d elec ode 9 whi ma ch i o a cale a spasihs p e a hl m be about wenty .thhusa dths o a c between th ah is and h scale a-h 2 The instrument which is illustrated has a substahti lly c indrica dia pla s and h s its po ts iiswhwaid hs a 2 n p d with the pointing end 23, hich is adjacent the hal he dial plate 2 h 9 1 embodihehts 0i the ih h oh h po nt might be a straight one and the scale night he carried direqily vis. he scale Pau The amount of spacing between the vane l9 and the sgale pan 20, which are parallel toeach other, depends onthe voltage which is to applied; and the spacing nsed as an example is suitable for a voltage of about 250 volts.

The-scale pan 2!! is connected by a conductor 24 is r stii r i th Q hs t rm a o which P RWQWQ 9 e $Qn O a ra srm h Ths ssindh tor i i sshns ted o i a limitin ssistshss 21 t th th r al Of he ss hiia 25 The es st n e 2i 'b' high ssi ahss f r defin ly imit n th mm izzurrent which may pass from vane 19 to plate Pl ts 2.9 prsierably ov es! w h an in sts r-shiiass. wh ch in som c s may be a iq izss u ia e alum num h a it sihsist 9 a ia sr o sshsisn sr ap r hsh ssi to this meta mate 72.0- The ihsuiated surface prevents the passage of current when he W4? is clamp d- .lh vans l is pva the purp s o rsas h the area o h isle ro tatic field .been the ram: an the p a e 20'- he plate 2;; preferably beveled at 28 or provided with hhsis QQ iQ G eliminating the electrostatic fiiiliil 9 i whi h take place at sharp corners sagas and tend to distort the field acting on the vane I9.

The vane I9 is also preferably slightly shorter than the radial width of the plate 20, which is arcuate in shape, having an inner concave surface 29 and an outer concentric convex surface 39. The radius on which the edges 29 and 39 are formed is substantially at the axis of the moving coil Ill.

The transformer 3| has its primary 32 connected to a suitable source of A. C., such as a 110 volt 60 cycle circuit through a relay 33.

Referring to Fig. 3, this shows the circuit without the relay and with the terminal connectors 34-39. Terminals 38 and 39 may lead to the usual current carryin springs 49 and 4| of the instrument movement for actuating the pointer responsive to temperature as determined by a.

thermocouple.

The conductors 42, 43 of the primary 32 may lead to the 60 cycle 110 volt line. The relay contact 44 is adapted to close that circuit at the fixed contacts 45, 49. The relay may be energized by means of a suitable battery 41 and controlled by a hand switch 48 or controlled responsive to some particular condition which is sought to be measured.

The operation of the present device is as follows: When the pointer has been moved by its moving coil element to indicate the number of degrees Fahrenheit which the user desires to measure, the relay circuit may be closed at 48, energizing the relay. This will close the contacts through the primary of the transformer 3i energizing the secondary; but the current output of the secondary is definitely limited by the limiting resistance 21 which, for example, may be one megohm; and the polarity of the current output is determined by the rectifier 25 in that circuit, which permits current to flow only in one direction.

The amount of current which flows is quite negligible, amounting only to that necessary to' charge the vane l9 and the plate 29, which are spaced from each other. The charging current, however, and voltage applied, amounting to about 250 to 260 volts, or any higher value, brings into existence an electrostatic field between the vane l9 and the plate 29.

The voltage may be either A. C. or D. C. and its magnitude would depend upon the geometry of the vane and spacing between the vane and plate.

These being oppositely charged, they are attracted to each other; and the pointer l4 being suificiently resilient, the vane 19 is drawn to the plate and effectively clamped in fixed position against the plate 29 because the returning springs are not sufficient to overcome the friction between the vane I9 and the plate 20 under this clamping force.

Thus the indication of temperature may be read at any time; and thereafter the relay circuit may again be opened at 48, opening the energizing circuit of the transformer and reducing to zero the electrostatic charges on the vane 19 and plate 20, which are discharged through the secondary 26.

The attractive force then ceases; and the pointer bends back to its original straight con-- dition, spacing the vane 19 from the plate 20 and permitting the pointer to swing freely again.-

It will thus be observed that I have invented an improved clamping arrangement for pointers of indicating instruments, by means of which 4 the clampin of the pointer may be easily controlled by electric circuits.

The present clamping arrangement is positive in its action, both in clamping and in releasing the pointer; and as the vane l9 may be made of aluminum, a minimum amountof weight is added. to the pointer. The sensitivity and the accuracy of the instrument are not materially affected by this arrangement.

While I have illustrated a preferred embodiment of my invention, many modifications may be made without departing from the spirit of the invention, and I do not wish to be limited to the precise details of construction set forth, but desire to avail myself of all changes within the scope of the appended claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States, is:

1. In an indicating instrument, the combination of a pointer and a moving element movable responsive to a condition to be measured, with a scale for indicating the measurement in connection with the pointer, a fixed conducting plate located adjacent the pointer and uniformly spaced from the pointer throughout a predetermined range of movement, a movable conducting plate carried by the pointer and spaced from but close to the first-mentioned conducting plate, insulation between said plates, and means for impressing a D. C. charge upon said plates of opposite polarity so that the two plates will be attracted to each other, and the pointer will be held by engagement of the two plates at any position in which it happens to be at the time the charge is applied.

2. In an indicating instrument, the combination of a pointer and a moving element movable responsive to a condition to be measured, with a scale for indicating the measurement in connection with the pointer, a fixed conducting plate located adjacent the pointer and uniformly spaced from the pointer throughout a predetermined range of movement, a movable conducting plate carried by the pointer and spaced from but close to the first-mentioned conducting plate, insulation between said plates, and means for impressing a D. C. charge upon said plates of opposite polarity so that the two plates will be attracted to each other, and the pointer will be held by engagement of the two plates at any position in which it happens to be at the time the charge is applied, the said movable plate comprising a light aluminum vane secured to the pointer.

3. In an indicating instrument, the combination of a pointer and a moving element movable responsive to a condition to be measured, with a scale for indicating the measurement in connection with the pointer, a fixed conducting plate located adjacent the pointer and uniformly spaced from the pointer throughout a predetermined range of movement, a movable conducting plate carried by the pointer and spaced from but close to the first-mentioned conducting plate, insulation between said plates, and means for impressing a D. C. charge upon said plates of opposite polarity so that the two plates will be attracted to each other, and the pointer will be held by engagement of the two plates at any position in which it happens to be at the time the charge is applied, the said means including fine insulated wire secured about the pointer and leading to a current conducting spring connected to a suitable terminal.

4. In a pointer clamping device for indicating instruments, the combination of an electrical instrument having a moving element and a pointer carried thereby, and a scale over which the pointer plays, an electrical conducting plate arranged parallel to the plane of movement of the pointer, and a light metal vane carried by the pointer in close proximity to but spaced from said plate, a thin layer of insulation between said vane and plate for preventing relatively high voltage discharge between them, and means for impressing a direct current charge on the plate and the vane of opposite polarity so that the vane is attracted to the plate, the pointer bending slightly until the vane engages the plate andis frictionally held against movement away from the indication which it is giving at the time it is attract'ed.

5. In a pointer clamping device for indicating instruments, the combination of an electrical instrument having a moving element and a pointer carried thereby, and a scale over which the pointer plays, an electrical conducting plate arranged parallel to the plane of movement of the pointer, and a light metal vane carried by the pointer in close proximity to but spaced from said plate, a thin layer of insulation between said vane and plate for preventing relatively high voltage discharge between them, and means for impressing a direct current charge on the plate and the vane of opposite polarity so that the vane is attracted to the plate, the pointer bending slightly until the vane engages the plate and is frictionally held against movement away from the indication which it is giving at the time it is attracted, said insulating layer comprising a layer of electrically insulating paper carried by the conducting plate.

6. In a pointer clamping device for indicating instruments, the combination of an electrical instrument having a moving element and a pointer carried thereby, and a scale over which the pointer plays, an electrical conducting plate arranged parallel to the plane of movement of the pointer, and a light metal vane carried by the pointer in close proximity to but spaced from said plate, a thin layer of insulation between said vane and plate for preventing relatively high voltage discharge between them, and means for impressing a direct current charge on the plate and the vane of opposite polarity so that the vane is attracted to the plate, the pointer bending slightly until the vane engages the plate and is frictionally held against movement away from the indication which it is giving at the time it is attracted, said means comprising a transformer having its secondary connected to the plate and vane through a rectifier, said transformer being controlled by a relay, a source of energization for said relay, and switching means for controlling the energization of the relay to apply the charge to said plate and vane.

7. In a pointer clamping device for indicating instruments, the combination of an electrical instrument having a moving element and a pointer carried thereby, and a scale over which the pointer plays, an electrical conducting plate arranged parallel to .the plane of movement of the pointer, and a light metal vane carried by the pointer in close proximity to but spaced from said plate, a thin layer of insulation between said vane and plate for preventing relatively high voltage discharge between them, and means for impressing a direct current charge on the plate and the vane of opposite polarity so that the vane is attractedto the plate, the pointer bending slightly until the vane engages the plate and is frictionally held against movement away from the indication which it is giving at the time it is attracted, the said plate being arcuate in shape and formed on a radius substantially equal to the distance from the plate to the axis of the pointer.

8. In an electric pointer clamp for indicating instruments, the combination of a support with an electrical instrument movement carried thereby, and having a movable element, said movable element carrying a resilient pointer, a scale plate, scale divisions, and indicia cooperating with said pointer to indicate the movement of the pointer, an arcuate electric conducting plate carried by said support and located closely beneath the sweep of the pointer, an electric conducting vane carried by said pointer adjacent to but out of contact with said plate, a thin, light electrical conductor extending along said pointer and connected to said pointer vane, a source of high potential direct current connected to said conductor and to said conducting plate, and a thin layer of insulation carried by said conducting plate on its face for preventing a short circuit between the vane and conducting plate, and switching means for controlling the application of said direct current, the direct current charging the vane and plate with static charges of opposite polarity, causing the vane to be attracted to the plate, the resilient pointer bending, and the vane coming into tight frictional engagement with the insulating layer on said plate to hold the pointer in the position in which it is indicating relative to the scale until released by release of the charges carried by said vane and plate.

ALFRED A. OBERMAIER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 554,275 Kelly Feb. 11, 1896 749,775 La Cour Jan. 19, 1904 1,415,528 Craighead May 9, 1922 FOREIGN PATENTS Number Country Date 447,242 Germany July 20, 1927 

